Multilayer pressure sensitive correction tapes are known. Such tapes are disclosed in U.S. Pat. Nos. 4,891,260 to Kunkel et al.; U.S. Pat. No. 5,221,577 to Inaba et al.; U.S. Pat. No. 5,700,552 to Katsuro et al.; U.S. Pat. No. 5,997,994 to Matsushima; U.S. Pat. No. 6,162,492 to Narayanan; and U.S. Pat. No. 6,235,364 to Katsuro et al. These multilayer flexible pressure sensitive correction tapes consist of a flexible carrier strip, a masking (cover) layer on the carrier strip, and an adhesive layer on the masking layer. The processes for preparing multilayer pressure sensitive correction tape have several features in common. The masking layer and pressure sensitive adhesive layer formulations contain pre-formed polymers when the formulations are applied to the correction tape assembly. Second, the formulations contain volatile solvents, typically organic solvents, and the formulations are applied as either solutions or dispersions. Third, the layers are developed by allowing the solvents to evaporate. One disadvantage of these solvent-based processes is that an initially applied layer will be susceptible to resolubilization when the second layer is applied to it. This could adversely affect the overall properties of the multilayer pressure sensitive correction tape.
A method of avoiding this problem is disclosed in U.S. Pat. No. 4,891,260 to Kunkel et al. U.S. Pat. No. 4,891,260 discloses a masking layer formulation containing a resin dissolved in an organic solvent. The masking layer is applied to the tape, and the solvent is removed by evaporation. The adhesive layer is then applied as an aqueous dispersion. This approach minimizes resolubilization of the underlying masking layer. However, the use of organic solvents on an industrial scale is not desirable. Such solvents are sources of pollution, so they are subject to environmental regulations. Measures taken to decrease the environmental impact of organic solvents increase production costs of correction tapes. Therefore there is an incentive to prepare correction tapes with reduced levels of organic solvents.
A multilayer pressure sensitive correction tape prepared with only aqueous solvents is disclosed in U.S. Pat. No. 6,162,492 to Narayanan. There both the adhesive and masking layers are applied as aqueous solutions or suspensions. However, the aqueous process disclosed in U.S. Pat. No. 6,162,492 may require the use of pH balancers, and the process still requires two evaporation steps. Such requirements add to the cost and complexity of the process.
In preparing pressure sensitive correction tapes by conventional solvent-based coating processes, the formulations for the layers are applied to the correction tape followed by evaporation. During this drying process the thickness of the applied film can decrease by a factor of about two. This makes it difficult to prepare a layer with a desired thickness.
A more desirable process for preparing a multilayer pressure sensitive a correction tape would use no solvent. Solvent-free processes for applying coating layers to substrates are known. U.S. Pat. No. 4,388,137 to McCarty et al. discloses a process for using radiation to facilitate the transfer of a coating vehicle to a substrate. The coating vehicle composition is first applied to a web carrier, and the coating composition is contacted with a porous substrate. The resulting “sandwich” (carrying web/uncured coating/substrate) is irradiated. The carrying web is peeled away, and the cured coating remains attached to the porous substrate. However, there is no disclosure that the radiation cured coating can function as a pressure sensitive adhesive.
U.S. Pat. No. 4,434,207 to Francy discloses a process for forming a highly cross-linked adhesive supported on a thin flexible substrate. The adhesive formulation is applied-directly to a tape without solvent, and is cured with radiation. However, the correction tape contains no covering layer or opaque blocking agents. Instead, the invention is used as a “lift-off” correction medium to remove ink from paper.
A slightly different process for preparing a pressure sensitive adhesive is disclosed in U.S. Pat. No. 5,194,455 to Massow et al. There a preformed, heat-flowable polymer formulation is melt-coated onto a tape. The coating is then irradiated with high energy radiation to form a pressure sensitive adhesive that is useful for industrial or medical adhesive tapes. However, there is no disclosure that the invention can additionally contain a masking layer between the pressure sensitive adhesive layer and the tape.
There is a need for a multilayer pressure sensitive correction tape which exhibits improved film toughness, improved resistance to ink “bleed through”, infusibility, and essentially no solubility in organic solvents or water.